Controllable fuel cell humidification by ultrasonic atomization

Compared with the conventional bubble-type humidifier used for PEMFC (proton exchange membrane fuel cell) humidification, ultrasonic atomization has the advantages of a small size, ease in refilling and changing temperature, and more importantly, controllable humidity. This study develops a unique ultrasonic atomization system that includes a gas heating pipe, an ultrasonic driving circuit, an ultrasonic atomizer, and humidity sensors. The reactive gases used are hydrogen and air. The gas humidity increases due to the ultrasonic micro water droplets that blend with the gases. The humidity is controlled by adjusting either the heating temperature or the driving voltage. In addition, the size of the micro water droplets can be manipulated by adjusting the driving frequency. An increased driving frequency leads to a smaller mean droplet diameter, which increases the humidification efficiency. A relative humidity of at least 90% can be maintained for gas flow rates between 1 and 25 LPM. The conventional bubble-type humidification can achieve only ∼80% relative humidity under the same conditions. The I-V curve also indicates that an optimal humidity is required for improved performance. Thus, a dynamic controllability of the humidification is important, especially for high-capacity FC (fuel cell) performance.